The present invention relates to a metallurgical container with a fragmented metallic enclosure, used for inductive treatment of metal and metal alloys, especially steel.
The practice of treatment of metal, and especially of steel, is directed more and more toward a metallurgy "outside a blast furnace," that is, "to a metallurgical process in a container." Such a solution runs against a delicate problem of heating metal in a container. The electric heating by induction has the advantage of transmitting the energy to the mix of the metallic charge with an excellent thermic output. Nevertheless, such heating creates undesirable Foucault currents in the metallic elements of the enclosure. From this results, that the enclosure is overheated, and that after a certain number of operations, it will loose its mechanical holding power due to excessive thermal strains. On the other hand, the enclosure of the container has to support strong pressures exercised by the molten metal.
Thus, it is necessary to produce a metallurgical container which satisfies two requirements: On the one hand, to avoid heating by Foucault currents of the parts which are placed within the magnetic heating field, and, on the other hand, to assure the mechanical strength of the metallurgical container.
In this respect, the French Pat. Nos. 2,366,079; 2,368,542; 2,368,543; 2,368,326 and 2,370,797, in the name of the inventor of the present invention, propose metallurgical containers of the type mentioned above. More specifically, French Pat. No. 2,370,797 describes a metallurgical container a vertical cross section of which is schematically illustrated in FIG. 1.
As can be seen from FIG. 1, the metallurgical container according to the prior art is provided with a refractory lining 1. The metallic enclosure 2 of the container is fragmented, and it is constituted, in the heat zone, that is with regard to the inductive winding 3, by metallic longitudinally extending tubular tie rods 4, constructed for the passage of a cooling fluid therethrough. The tubular tie rods 4 are maintained in place between two annular flanges, that is the upper flange 5 and the lower flange 5', which are respectively rigidly connected to a sleeve 6 and to the bottom 7 of the container.
The sleeve 6 serves to hoop or surround the refractory lining 1 at an upper end portion thereof, and it includes two rings, that is the upper ring 8 and the lower ring 9 fixedly connected thereto, wherein the lower ring 9 serves to support the container at the time of its installation and means for induction heating.
The tie rods 4 are connected to the flanges 5 and 5' by connecting means 10 so as to present an internal axial passage 11 which is connected through the ring 9 in the zone 12 defined between the rings 8 and 9 by means of the connecting means 10 and a fluid-tight extension 13. The cooling fluid is introduced at the lower end of the tie rods 4, passes successively through the passage 11, the connecting means 10, the fluid-tight extension 13, and escapes in the zone 12.
The inventor has studied the thermic evolution of the metallic members of a metallurgical container of this type during the intensive treatment by inductive heating. Indeed, it is necessary to effect an extensive heating treatment, that is a treatment in which high electric currents are used and the duration of the heating is extended. On the other hand, during such treatments, it is necessary to avoid excessive heating of the metallic elements of the metallurgical container.
In order to study the thermic evolution, five thermoelectric couples have been placed at different points of the metallurgical container, that is at the points A, B, C, D and E as indicated in FIG. 1. FIG. 2 represents the results of this study.
In FIG. 2, the various curves indicate the temperature (in centigrade) as a function of time (in hours) for the different points A, B, C, D and E of the container.
As can be seen from these curves, the highest temperature of the container (450.degree. C.) is obtained at the upper flange 5, and even though the same is outside of the heating zone. The temperature reached at the lower flange 5' and at the sleeve 6 is essentially lower (350.degree. C.). The temperature at the bottom 7 and that of the tie rods 4 is lowest (150.degree. C.), which confirms the efficiency of the internal cooling described above.
These studies have shown that the metallurgical container of the prior art described above is usable for medium heating but that, for a more forceful heating, the thermic strains from rapid heating of the flanges will create serious problems.